This invention relates to a display system with a linear array of electromechanical grating modulators that is scanned in order to generate a two-dimensional image. More particularly, the invention relates to an electromechanical grating display system that has spatially separated diffracted light beams throughout the system.
Electromechanical spatial light modulators with a variety of designs have been used in applications such as display, optical processing, printing, optical data storage and spectroscopy. These modulators produce spatial variations in the phase and/or amplitude of an incident light beam using arrays of individually addressable devices.
Spatial phase modulation of an incident beam can be accomplished by arrays of individually addressable deformable mirrors. Such devices can be made by suspending a deformable reflective membrane over a grid of supports, as described U.S. Pat. No. 4,441,791 issued Apr. 10, 1984 to Hornbeck entitled Deformable Mirror Light Modulator. However, because of the membrane and support structure, these particular deformable mirrors are very inefficient. More efficient deformable mirror designs are disclosed in U.S. Pat. No. 5,170,283 issued Dec. 8, 1992 to O""Brien et al. entitled Silicon Spatial Light Modulator, and in U.S. Pat. No. 5,844,711 issued Dec. 1, 1998 to Long, Jr. entitled Tunable Spatial Light Modulator.
Another class of electromechanical spatial light modulators has devices with a periodic sequence of reflective elements that form electromechanical phase gratings. In such devices, the incident light beam is selectively reflected or diffracted into a number of light beams of discrete orders. Depending on the application, one or more of these diffracted light beams may be collected and used by the optical system. For many applications, electromechanical phase gratings are preferable to deformable mirrors. Electromechanical phase gratings can be formed in metallized elastomer gels; see U.S. Pat. No. 4,626,920 issued Dec. 2, 1986 to Glenn entitled Solid State Light Modulator Structure, and U.S. Pat. No. 4,857,978 issued Aug. 15, 1989 to Goldburt et al. entitled Solid State Light Modulator Incorporating Metallized Gel and Method of Metallization. The electrodes below the elastomer are patterned so that the application of a voltage deforms the elastomer producing a nearly sinusoidal phase grating. These types of devices have been successfully used in color projection displays; see Metallized viscoelastic control layers for light-valve projection displays, by Brinker et al., Displays 16, 1994, pp. 13-20, and Full-colour diffraction-based optical system for light-valve projection displays, by Roder et al., Displays 16, 1995, pp. 27-34.
An electromechanical phase grating with a much faster response time can be made of suspended micromechanical ribbon elements, as described in U.S. Pat. No. 5,311,360 issued May 10, 1994 to Bloom et al. entitled Method and Apparatus for Modulating a Light Beam. This device, also known as a grating light valve (GLV), can be fabricated with CMOS-like processes on silicon. Improvements in the device were later described by Bloom et al. that included: 1) patterned raised areas beneath the ribbons to minimize contact area to obviate stiction between the ribbons and the substrate, and 2) an alternative device design in which the spacing between ribbons was decreased and alternate ribbons were actuated to produce good contrast; see U.S. Pat. No. 5,459,610 issued Oct. 17, 1995 entitled Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction between Grating Elements and Underlying Substrate. Bloom et al. also presented a method for fabricating the device; see U.S. Pat. No. 5,677,783 issued Oct. 14, 1997 entitled Method of Making a Deformable Grating Apparatus for Modulating a Light Beam and Including Means for Obviating Stiction Between Grating Elements and Underlying Substrate. Additional improvements in the design and fabrication of the GLV were described in U.S. Pat. No. 5,841,579 issued Nov. 24, 1998 to Bloom et al. entitled Flat Diffraction Grating Light Valve, and in U.S. Pat. No. 5,661,592 issued Aug. 26, 1997 to Bornstein et al. entitled Method of Making and an Apparatus for a Flat Diffraction Grating Light Valve.
For display or printing, linear arrays of GLV devices can be used with a scanning Schlieren optical system as described in U.S. Pat. No. 5,982,553 issued Nov. 9, 1999 to Bloom et al. entitled Display Device Incorporating One-Dimensional Grating Light-Valve Array. Alternatively, an interferometric optical system can be used to display an image as disclosed in U.S. Pat. No 6,088,102 issued Jul. 11, 2000 to Manhart entitled Display Apparatus Including Grating Light-Valve Array and Interferometric Optical System. In the scanning Schlieren display system of Bloom et al. ""553, the plane of diffraction, which contains the diffracted light beams, is parallel to the axis of the linear GLV array because the grating period is parallel to the axis. This increases the cost and complexity of the display system. Specifically, efficient collection of the primary diffracted light beams requires at least one dimension of the optical elements to be significantly larger than the extent of the linear GLV array. Furthermore, the diffracted and reflected light beams overlap spatially throughout most of the optical system. Separation of diffracted light from reflected light is accomplished in close proximity to a Fourier plane of the Schlieren optical system. However, the Fourier plane is usually also the preferred location of a scanning mirror for producing a two-dimensional image.
Recently, a linear array of electromechanical conformal grating devices was disclosed by Kowarz in U.S. Ser. No. 09/491,354 filed Jan. 26, 2000 now U.S. Pat. No. 6,307,663. For this type of device, it is preferable to have the grating period perpendicular to the axis of the linear array. The diffracted light beams are then spatially separated throughout most of the optical system. In U.S. Ser. No. 09/491,354 now U.S. Pat. No. 6,307,663, it was mentioned that a simplified display system is possible to use with a new device. However, no specific description of the display system was given. There is a need therefore for a scanning display system that utilizes a linear array of electromechanical conformal grating devices. Furthermore, there is a need for a system that is simpler and less costly than prior art systems.
The need is met according to the present invention by providing a display system that includes a light source for providing illumination; a linear array of electromechanical grating devices of at least two individually operable devices receiving the illumination, wherein a grating period is oriented at a predetermined angle with respect to an axis of the linear array wherein the angle is large enough to separate diffracted light beams prior to a lens system for projecting light onto a screen; an obstructing element for blocking a discrete number of diffracted light beams from reaching the screen; a scanning element for moving non-obstructed diffracted light beams on the screen; and a controller for providing a data stream to the individually operable devices.
The present invention has several advantages, including: 1) improvement in contrast by eliminating reflections from projection lens, because of the new flexibility in placing the turning mirror between the linear array and the projection lens; 2) reduction in size of the scanning mirror, because now the scanning mirror can be placed directly at the Fourier plane; 3) increase in design flexibility, because now separation of diffracted orders can take place almost anywhere in the system, not just at the Fourier plane; and 4) reduction in size of lenses and other optical elements.